October 5, 2012

Lakes Are Still Processing Ancient Carbon Stores

A new study is challenging current models of long-term carbon storage in lakes and rivers by revealing that a significant amount of carbon released into the atmosphere from lakes and rivers in Southern Quebec, Canada is approximately 1,000 to 3,000 years old.

Current models and previous studies have shown there to be a tight coupling between the terrestrial and aquatic environment. So tight, in fact, that they expect aquatic bacteria to be rapidly consuming modern carbon. The findings of the new study, published in Proceedings of the National Academy of Sciences, showing the respiration of old carbon in aquatic systems suggest there may be significant lags in the coupling between terrestrial and aquatic systems. Further, this represents an additional and unaccounted for source of carbon dioxide to the atmosphere.

Though it is well established that bacteria in northern waters process carbon from their terrestrial surroundings, the research team from Virginia Commonwealth University and the Universite du Quebec a Montreal challenge the belief that older carbon sources are not available to bacteria and have been mostly removed from the carbon feedback loop between earth and air.

The scientists used radiocarbon dating to determine the age of carbon respired by bacteria and released as carbon dioxide. What they found is that some of the carbon consumed dated as far back as 1,000 to 3,000 years old.

Though the findings are regional, the team notes that if most northern waterways are also selectively processing older carbon, the global output from these ancient sources could well be significant. As a greenhouse gas, an increase in carbon dioxide in the atmosphere provides a positive, or amplified, feedback to climate change.

“While it is not clear if this release of ancient carbon is new or related to anthropogenic climate change, it supplies an additional source of carbon dioxide to the atmosphere,” said S. Leigh McCallister, assistant professor of biology at VCU.

“This study illustrates the need to incorporate the potential processing of pre-aged, or older, carbon sources into current carbon models,” she said.